Down syndrome (DS) or trisomy 21 (Ts21) is caused by the presence of three copies of chromosome 21, and is the most frequent genetic cause of mental retardation. The Ts65Dn trisomic mouse has recently been developed and is trisomic only for the segment of murine chromosome 16 that is homologous to the segment of human chromosome 21 thought to contribute to mental retardation and vulnerability to Alzheimer disease in DS. This mouse demonstrates abnormal behavior and is impaired in various learning paradigms. We demonstrated that long-term potentiation (LTP) and long- term depression (LTD) decrease and increase respectively in the CAl region of the Ts65Dn mouse of Ts65Dn mouse hippocampus. The objective of this proposal is to find mechanisms that cause the abnormal LTP and LTD. Three specific aims are proposed to test that abnormal LTP and LTD are due to changes in signal transduction pathways mediated by protein kinase A (PKA) and/or protein kinase C (PKC) that would cause posttranslational changes in voltage-dependent Na+, Ca2+ channels and NMDA-, AMPA-glutamate receptors and cause changes in synaptic activity in the hippocampus. Aim#1: Determine PKA pathway activity in Ts65Dn hippocampus in relation to LTP and LTD paradigm. Determine expression of phosphorylated CREB. Aim #2:PKC activity in Ts65Dn hippocampus in relation to LTP and LTD paradigm. Determine expression pattern of PKC isoforms. Aim #3:Determine the expression and posttranslational modification of voltage dependent Na+, Ca2+ channels and NMDA -, AMPA- glutamate receptors using nucleated patch-clamp recording technique and binding studies. The impact of PKC isoforms will be tested in cell lines that permanently over express Na+ channel, Ca2+ channels, NMDA and AMPA receptors. Signal transduction impairments in genetic model of DS will determine important targets for treatment of mental retardation. In addition the outcome of this research will include further understanding of the role of PKA and PKC and voltage-dependent channels and NMDA- and AMPA-receptors in the mechanisms that are behind LTP and LTD.